Timings
The data throughput of the M48A is limited by the radio path. In continuously streaming (transparent) mode a
baud rate of 4800 baud is supported without any buffer overflows.
Byte latency is influenced by the switching performance of the radio (and the programmed DELAY and
PREAM values).
In default mode (20mS delay, 50mS preamble) the single byte in to out latency is of the order of 110mS
(20+50+40mS burst length and processing delays) although in streaming data this is reduced to around
30mS
If radio switching times are faster, then the preamble duration and the tx off delay can be reduced (crystal
controlled radios such as NiM2 work well with 15mS of preamble, 5mS tx off) and latency falls to around
40mS
In ANK mode, the switching speed of the radios, and the time absorbed in sending and decoding the
acknowledge burst dominate the data throughput. The acknowledge in itself requires only 20mS, but the
requirement to switch both radios between receive and transmit (to send the data packet, and then the akn
packet) adds a significant overhead.
Referring to the default timing setup this results in 1 packet per 150mS, and a peak data throughput of only
900 baud, although if radios with faster switching performance are used then this is significantly increased.
(With NiM2 or BiM1 radios, the preamble duration can be significantly reduced, and an acknowledged mode
data rate of well over 1200 baud is achievable)
Unless only short data bursts are used, we recommend the use of CTS flow control if AKN is selected
RS485 to RS232 Adaptor
Figure 3: RS485 to RS232 Adaptor connections
M48 Applications Board can be supplied with RS232 DB9F, 2.1mm DC Jack connectors replaced with 3-wire
RS485 to RS232 Adaptor and power terminal blocks.
http://www.ti.com/lit/ds/symlink/ds3695.pdf
Jumper Link JP13 is provided for 120Ω termination.
USB-RS485-WE-1800-BT adaptor cable can be used to evaluate M48 RS485 Application Board on a
PC/laptop running HyperTerminal Terminal Emulation Program via virtual COM serial port.
http://www.ftdichip.com/Products/Cables/USBRS485.htm
http://www.hilgraeve.com/hyperterminal/
Radiometrix Ltd, M48A Apps board Manual
page 9
RADIOMETRIX [ RADIOMETRIX LTD ]
